Metal guard rings are commonly provided around the peripheral of a die. The guard rings serves as, for example, moisture barriers, crack stops or grounds. Different guard rings can be provided for different purposes. FIG. 1 shows a die 100 with guard rings 120 and 140 formed at the periphery of a die 100. For example, the outer guard ring serves as a crack stop while the inner guard ring serves as a moisture barrier. As shown, the outer guard ring is rectangular in shape while the inner guard ring has 45° angles 145 at the corner of the die, forming an octagon-shaped guard ring. Typically, each guard ring can include a plurality of rings or sub-rings. For example, a guard ring may have 5 sub-rings.
The guard rings are formed in the via levels of the die. For example, as shown in FIG. 2a, trenches 228 are etched in the interlevel dielectric layer 209 on a substrate 201 at the periphery of the die along with vias 260. The critical dimension CD for guard rings is the same as that for vias. Due to micro-loading effects, trench etch rate is faster than via etch rate. The difference in etch rates is even more prominent for low-K dielectric materials. This results in the trench punching through the barrier 265 below the interlevel dielectric. FIG. 2b shows a SEM evidencing the difference in etch rate between vias 260 and trenches 228. The trench etch rate is about 10-20% faster than the via etch, resulting in trench depth of about 1.8 Å deeper than the vias. Punching through the barrier layer may undesirably result in L-arcing which leads to etch defects such as particle and ball defects, negatively impacting yield.
From the foregoing, it is desirable to prevent the effects of micro-loading within ICs and improve reliability during production of ICs so as to improve yield when improvising guard rings within the IC design.